A transfer press machines including a plurality of process stations in a press main body is typically provided with a workpiece transfer apparatus that sequentially transfers a workpiece to a subsequent step in process steps.
The workpiece transfer apparatus is provided with a pair of transfer bars that are parallel to a workpiece transfer direction. On each of the transfer bars, a plurality of work holders are detachably provided in a manner to correspond to upper dies and lower dies. The workpiece is sequentially transferred from a position of a die on the upstream side to a position of a die on the downstream side by a three-dimensional movement operation of the transfer bar. The three-dimensional movement operation includes: feed/return directional movement in which the transfer bar is reciprocated in a feed direction, which is the same direction as a workpiece transfer direction; lift/down directional movement (raising/lowering movement) in which the transfer bar is reciprocated in a lift direction (vertical direction); and clamp/unclamp directional movement in which the transfer bar is reciprocated in a clamp direction perpendicular to the feed direction on a horizontal plane.
In such a workpiece transfer apparatus, a workpiece transfer apparatus including the following components has been known as one particularly for moving the transfer bar in the clamp direction and raising/lowering the transfer bar (see, for instance, Patent Literature 1).
Specifically, the workpiece transfer apparatus includes: a first carrier that is movable in the clamp direction; a second carrier that is movable in the clamp direction independent of the first carrier; a first carrier driving mechanism (a ball screw and an electric motor that drives the ball screw) that drives the first carrier in the clamp direction; a second carrier driving mechanism (a ball screw and an electric motor that drives the ball screw) that drives the second carrier in the clamp direction; a parallel link that includes a first link and a second link, connects the first carrier to a support for supporting the transfer bar and are rotatable around a connector between the parallel link and the first carrier and a connector between the parallel link and the support; and a driving link that connects the first link of the parallel link to the second carrier and is rotatable around a connector between the driving link and the first link and a connector between the driving link and the second carrier.
In the workpiece transfer apparatus disclosed in Patent Literature 1, the ball screws of the first and second carrier driving mechanisms are driven by the electric motor, whereby the first and second carriers are reciprocated in the clamp direction, so that the transfer bar provided over the parallel link via the support is also reciprocated in the clamp direction. A clamp-directional movement of the first carrier and that of the second carrier are differentiated in speed, the first carrier having the connectors to the parallel link, the second carrier having the connector to the driving link. With this arrangement, inclination angles of the parallel link and the driving link are changed, so that the transfer bar over the parallel link can be raised/lowered.
As an apparatus that enables the transfer bar to move in three dimensions as described above, an apparatus including a feed driving device that moves the transfer bar in the feed direction, a lift driving device that moves the transfer bar in the lift direction, and a clamp driving device that moves the transfer bar in the clamp direction, has been known (see, for instance, Patent Literature 2).
In the workpiece transfer apparatus disclosed in Patent Literature 2, a lift driving device includes a lift screw (a ball screw) extending in the lift direction. The lift screw is rotated by a lift driving motor, whereby a lift carrier screwed to the lift screw is driven in the lift direction. A clamp driving device includes a lift screw (a ball screw) extending in the clamp direction. The clamp screw is rotated by a clamp driving motor, whereby a clamp carrier screwed to the clamp screw is driven in the clamp direction. A feed driving device includes a linear guide capable of supporting the transfer bar. The transfer bar guided by the linear guide is driven by a linear motor in the linear direction. The clamp driving device is attached to the lift driving device, and the linear driving device is attached to the clamp driving device, which enables three-dimensional movement of the transfer bar.